For the purpose of achieving a maximum degree of brightness, the paper industry has various methods at its disposal, such as selecting very bright paper raw materials, bleaching the raw material, and using fillers or white pigments, tinting dyes and/or optical brighteners. The optical brighteners do not hide the conventional yellowish shade of the paper by subtraction but substitute for the lack of remission by emitting additional fluorescent light. Optical brighteners shift the shade of the brightened material, e.g., from yellow towards blue, and the increase in emission results in an increase in brightness.
In the production of paper, it is usual to employ retention agents, dewatering agents, and/or fixatives to improve the speed of production or other properties and yield of the product. These adjuvants are mostly of cationic character. OBAs, by contrast, can be anionic in character. In paper processing, it is possible that the anionic and cationic substances (such as the retention agent and the OBA) could interact and form an undesirable precipitate. Furthermore, ionic interaction of OBAs with other substances such as retention agents can cause a discoloration in the appearance of the paper, making the product appear more “green” than if the OBA-containing paper did not involve a substance undergoing an ionic interaction with the OBA. In addition, certain OBAs do not bond well to the paper fibers, and are poorly retained.
There remains a need in the art, therefore, for a retention agent system that enhances the attachment of OBAs to paper fibers without impairing other desirable characteristics of the final paper product. Moreover, there exists a need in the art to improve OBA retention so as to reduce the loss of these expensive agents during paper processing.